THE MERCK VETERINARY MANUAL
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Disorders of the Carpus and Metacarpus in Horses

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The carpus involves 3 articulations—the radiocarpal (antebrachiocarpal), intercarpal (middle carpal), and carpometacarpal joints. Problems are localized to the carpal area based on lameness (including characteristic gait), swelling, synovial effusion and pain on palpation, and responses to flexion and diagnostic analgesia. The only clinical evidence of carpal problems may be synovial effusion and minor gait deficits. Visualization and palpation are important to determine the site of swelling in the carpus (eg, synovial fluid in the joint or tendon sheath or swelling in the subcutaneous space). Light palpation with fingers with the horse standing is useful initially. Synovial fluid accumulations tend to be more difficult to ascertain when the leg is picked up. Knowledge of the normal anatomic boundaries of the structures is important. The individual carpal bones can be assessed with the carpus flexed; direct palpation of lesions often elicits pain and the degree of carpal flexion possible may be noted.

Diagnostic analgesia of the carpal joints is usually done intra-articularly. The antebrachiocarpal and middle carpal joints can be injected easily. The carpometacarpal joint communicates with the middle carpal joint; therefore, local analgesia in the middle carpal joint provides analgesia to the carpometacarpal joint. There is considerable distal outpouching of the carpometa-carpal joint, and with time, analgesia will diffuse into the area of the proximal suspensory ligament.

Radiography of the carpus is critical for specific diagnosis of intra-articular fractures, osteochondritis dissecans, subchondral cystic lesions, osteoarthritis, septic arthritis, and osteochondroma of the distal radius.

Last full review/revision March 2012 by C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS, DACVSMR

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